Wafer Division Laser Focal Height Control
Solution Overview
Problem
Conventional laser processing methods for wafer division often result in cracking or chipping at the corner edges of chips due to the formation of weak modified layers at intersections of crossing streets.
Innovation Solution
A wafer processing method involving the formation of first and second modified layers at specific heights within the wafer, where the second modified layer is formed at intersections to avoid crack generation positions, using a laser beam with a transmission wavelength and an expand tape to guide the processing, allowing for controlled division without cracking or chipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a laser beam is applied along crossing streets to form modified layers for wafer division, then cutting waste is reduced and street width is minimized, but cracking or chipping occurs at corner edges of chips
Solution Approach 1:
The patent divides the laser processing into two separate stages: first forming modified layers along streets, then forming additional modified layers at intersections. This segmentation of the processing sequence allows each stage to address specific requirements without compromising the other, preventing cracks at intersections while maintaining clean street divisions.
Solution Approach 2:
The patent performs preliminary laser processing along the streets to form first modified layers before addressing the intersections. By preparing the street paths first and then adding intersection modifications, the process ensures that corner edges have proper crack initiation points without compromising chip integrity during subsequent division.
2Ease of manufacture
If modified layers are formed at all intersections of crossing streets, then wafer division is facilitated, but cracking starts at corner edges of chips
Solution Approach 1:
The patent applies different laser processing parameters and sequences to different locations: street areas receive one type of modified layer formation while intersection areas receive additional or different modified layers. This local differentiation ensures that each region has the appropriate crack initiation characteristics for its specific function, preventing corner edge cracking while maintaining division ease.
Solution Approach 2:
The patent changes laser processing parameters (such as focal position, power, or scanning speed) when forming modified layers at intersections compared to street areas. By adjusting these parameters, the modified layers at intersections provide proper division initiation without creating excessive stress concentration that would cause corner edge cracking.
3Device complexity
If laser beam focal point is set at a single height for all streets and intersections, then processing is simplified, but cracks generate at corner edges
Solution Approach 1:
The patent implements dynamic adjustment of the laser focal point height during processing. The focal position is varied depending on whether the laser is processing street areas or intersection areas, allowing optimized modified layer formation at each location while maintaining a relatively simple overall processing system.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively prevents cracking or chipping at the corner edges of chips by forming modified layers at heights that do not coincide with crack initiation points, ensuring precise and reliable division of wafers into individual device chips.
Implementation Method 1
applying a laser beam from a back side of the wafer to form first modified layers inside the wafer at a first height
Implementation Method 2
setting the focal point of a laser beam having a transmission wavelength to the wafer at a first height from the front side of the wafer
Implementation Method 3
an expand tape attaching step of attaching an expand tape to the front side of the wafer
Data Source
AI summary
A wafer processing method of dividing a wafer along a plurality of crossing streets formed on the wafer to obtain individual chips. The wafer processing method includes a modified layer forming step of applying a laser beam having a transmission wavelength to the wafer along each street to thereby form a modified layer inside the wafer and a dividing step of applying an external force to the wafer to thereby divide the wafer into the individual chips along each street with the modified layer functioning as a division start point. In the modified layer forming step, the modified layer is formed at each intersection of the crossing streets at a height where cracking can be avoided on the corner edges of each chip obtained by dividing the wafer.